Various types of vehicles have been developed to sweep or vacuum debris from pavements, roadways, and streets. In general, these vehicles can be classified as mechanical broom sweepers, air sweepers, and combinational variants thereof.
Mechanical broom sweepers use a motor-driven broom or brooms to mechanically sweep paper, plastic, litter, trash, vegetation (leaves, twigs, grass clippings, etc.), asphalt and concrete debris, and larger sand or gravel particles toward a conveyor for transport into a debris collection hopper.
Regenerative air sweepers use a motor-driven fan to create a high-velocity recirculating air flow to aspirate dust, particulates, and other debris from the pavement or street surface through an intake or pickup hood carried or suspended beneath the sweeper vehicle. Optionally, a gutter broom is often mounted adjacent one or both lateral sides of the intake hood to brush debris into the path of the intake hood, and a powered brush roll can be mounted with or contained within the intake hood to assist in dislodging particulates from the swept surface for entrainment into the air flow.
In a typical regenerative system, a motor-driven fan develops a high-volume, high-velocity recirculating air-flow through an intake or pickup hood that is positioned on or closely adjacent the pavement surface. As the intake hood is moved along the pavement surface, debris is aspirated into the air flow and carried by ducting into and through a debris-collecting hopper or container. As the debris-laden air enters the debris-collecting hopper, the velocity of the air flow is reduced sufficiently so that many particulates drop out the air stream with various types of baffles, screens, grates, panels, etc. causing additional particulates to drop out of the air flow and collect in the hopper.
It is known that some of the air flow in the intake hood can escape from beneath one or more of the various sides of the hood into the ambient environment; that escaping air flow can carry entrained particulates, known as ‘fugitive’ particles, into the ambient environment and undesirably contribute to the concentration of airborne particulates surrounding the cleaning vehicle. The issue of fugitive particles has been addressed by placing one or more elastomeric flaps or curtains along the perimeter edges of the intake hood; the flaps or curtains extend from the edges of the intake hood to the ground surface being sweep to minimize or otherwise limit the escape of fugitive air flows. Additionally, some systems are designed to vent some of the pressurized filtered air into the atmosphere prior to introduction into the intake hood to create a situation in which ambient make-up air is drawn into the intake hood to militate against the release of fugitive particulates. Since the volume of air introduced into the intake hood is large and the overall velocity of the primary air flow is large, subsidiary air flows can nonetheless be established that escape from beneath the intake hood.